This invention relates generally to a sensing system for detecting and measuring a constituent, such as oxygen, within a fluid, and more particularly, for detecting oxygen concentration levels in aqueous samples, gaseous samples, and biological samples.
A know method of measuring oxygen involves use of sensors applying lifetime/phase shift measurement techniques. Lifetime/phase shift measurement techniques generally provide, after proper calibration and provided there is a threshold level of light intensity being supplied to a sensor, a relatively absolute output correlating to concentration of oxygen. Variations in intensity above that threshold level ordinarily have little or no effect on the output of such lifetime/phase shift sensor.
However, disadvantages of lifetime/phase shift sensors ordinarily include a potential for degradation of the sensor over time, due to photo-bleaching of the sensor material. Accordingly, accommodations must be made for rejecting unwarranted ambient light from the sensor. Another potential disadvantage of the lifetime/phase shift-type sensor is that due to the typical inherent high-frequency operation of the probe, the sensor is of a certain sophistication, which may increase costs and manufacturing complexities. Also, high frequency operation of the probe typically requires accommodation for noise isolation, dielectric problems, interference, etc.
Also, with such lifetime/phase shift-type sensors, as oxygen increases, the signal-to-noise ratio may increase to the point where the signal is no longer obtainable, since the intensity threshold is below that which will give a meaningful lifetime/phase shift measurement.